# Golang Logging

> Standards for structured logging and observability in Golang. Use when adding structured logging or tracing to Go services.

- Skill: `hoangnguyen0403/golang-logging` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds add hoangnguyen0403/golang-logging`
- Raw SKILL.md: https://api.skillmd.com/api/skills/hoangnguyen0403/golang-logging/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: HoangNguyen0403 (https://skillmd.com/u/hoangnguyen0403)
- Updated: 2026-08-19
- Page: https://skillmd.com/skills/hoangnguyen0403/golang-logging

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# Golang Logging Standards

## **Priority: P1 (HIGH)**

## Principles

- **Structured Logging**: Use JSON or structured text. Readable by machines and humans.
- **Leveled Logging**: Debug, Info, Warn, Error.
- **Contextual**: Include correlation IDs (TraceID, RequestID) in logs.
- **No `log.Fatal`**: Avoid terminating app inside libraries. Return error instead. Only `main` should exit.

## Libraries

- **`log/slog` (Recommended)**: Stdlib since Go 1.21. Fast, structured, zero-dep.
- **Zap (`uber-go/zap`)**: High performance, good if pre-1.21 or extreme throughput needed.
- **Zerolog**: Zero allocation, fast JSON logger.

## Workflow: Set Up Structured Logging with slog

1. Create JSON handler at startup in `main()`
2. Optionally wrap in middleware to inject request-scoped attributes
3. Use `slog.With()` to add correlation IDs per request
4. Pass logger via context or dependency injection

See [slog setup and usage examples](references/slog-patterns.md)

## References

- [Slog Patterns](references/slog-patterns.md)

## Anti-Patterns

- **No fmt.Println in production**: Use slog or zap for structured, leveled logging.
- **No log.Fatal in libraries**: Return errors; only main() should call os.Exit.
- **No unstructured log strings**: Include correlation IDs and structured fields via slog.Attr.